Controlling Coordination Number of Rhodium(III) Complex by Ligand-Based Redox for Catalytic C–H Amination

Abstract

Abstract The rhodium (III) complexes supported by a di-deprotonated o-phenylenediamido ligand, ([Cp*RhIII(C6H4N2tBu2Ph22−)] ([Cp*RhIII(L2−)], 1), and one-electron and two-electron oxidized ligands, [Cp*RhIII(C6H4N2tBu2Ph2•−)(CN)] ([Cp*RhIII(L•−)(CN)], 2) and [Cp*RhIII(C6H4N2tBu2Ph20)(CN)]+ ([Cp*RhIII(L0)(CN)]+, 3) (H2L = H2C6H4N2tBu2Ph2 = N,N-di-(3,5-di-tert-butylphenyl)benzene-1,2-diamine)), have been synthesized and characterized by 1H NMR, ESI–mass, EPR, UV-vis spectroscopic methods, and cyclic voltammetry as well as single-crystal structure analysis. In complexes 2 and 3, a cyanide ion coordinates to each rhodium(III) center to stabilize the six-coordinate structures. Catalytic activity of these complexes has been examined in the intramolecular C–H amination of trisylazide (2,4,6-triisopropylphenylsulfonyl azide) to find that complex 2 shows the highest activity. The result suggests that single-electron transfer takes place from the anion radical ligand C6H4N2tBu2Ph2•− of 2 to trisylazide to form a nitrene radical bound rhodium(III) active species for the C–H amination.